FIX/CI: Support installing from Git URLs

[bocklund]

When installing ESPEI from a git source using package managers, e.g.

pip install git+https://github.com/phasesresearchlab/espei.git@master

or entirely from a fresh env using uv:

uv init --bare
uv add "espei @ git+https://github.com/phasesresearchlab/espei.git@master"

the code can successfully install, but give errors like this when you try to use it:

Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    import espei
  File "/Users/bocklund1/src/test/.venv/lib/python3.13/site-packages/espei/__init__.py", line 10, in <module>
    __version__ = get_version(root='..', relative_to=__file__)
  File "/Users/bocklund1/src/test/.venv/lib/python3.13/site-packages/setuptools_scm/_get_version.py", line 56, in get_version
    return _get_version_public(
        root=root,
    ...<17 lines>...
        scm=scm,
    )
  File "/Users/bocklund1/src/test/.venv/lib/python3.13/site-packages/vcs_versioning/_get_version_impl.py", line 257, in get_version
    _version_missing(config)
    ~~~~~~~~~~~~~~~~^^^^^^^^
  File "/Users/bocklund1/src/test/.venv/lib/python3.13/site-packages/vcs_versioning/_get_version_impl.py", line 207, in _version_missing
    raise LookupError(error_msg)
LookupError: setuptools-scm was unable to detect version for /Users/bocklund1/src/test/.venv/lib/python3.13/site-packages.

Make sure you're either building from a fully intact git repository or PyPI tarballs. Most other sources (such as GitHub's tarballs, a git checkout without the .git folder) don't contain the necessary metadata and will not work.

For example, if you're using pip, instead of https://github.com/user/proj/archive/master.zip use git+https://github.com/user/proj.git#egg=proj

Alternatively, set the version with the environment variable SETUPTOOLS_SCM_PRETEND_VERSION_FOR_${NORMALIZED_DIST_NAME} as described in https://setuptools-scm.readthedocs.io/en/latest/config/

Looking at

# espei/__init__.py
try:
    from ._dev import get_version
    # We have a local (editable) installation and can get the version based on the
    # source control management system at the project root.
    __version__ = get_version(root='..', relative_to=__file__)
    del get_version
except ImportError:
    # Fall back on the metadata of the installed package
    from importlib.metadata import version
    __version__ = version("espei")
    del version

There current behavior of __init__.py expects one of the following cases:

1. Installing from a release version that has a sdist/bdist where MANIFEST.in does prune espei/_dev and therefore ._dev doesn't exist and we hit the ImportError fallback to importlib.metadata
2. For working from the git source checkout, you have full git history and get_version from setuptools_scm detects the git tag and can set the versions correctly.

However, when installing on one of the failure modes above, you get an in between case where
a) you get all the files, which includes _dev/__init__.py, and
b) you don't get the full git repo with the full git version history

and thus you don't get the ImportError, but you have setuptools_scm.get_version raise a LookupError when it fails.

This PR catches that LookupError and falls back onto the importlib.metadata version which does work on installs using the git+ mechanism above on pip and uv. It also adds a new GitHub Action file for doing smoke tests, where in this case we add a single test that installing ESPEI to a bare repo and then importing works.

This should fix issues in getting CI working in downstream packages like here: materialsgenomefoundation/kawin#19